U.S. patent number 11,380,989 [Application Number 16/676,895] was granted by the patent office on 2022-07-05 for method to optimally reduce antenna array grating lobes on a conformal surface.
This patent grant is currently assigned to The Boeing Company. The grantee listed for this patent is The Boeing Company. Invention is credited to Ted R. Dabrowski, John Dalton Williams.
United States Patent |
11,380,989 |
Dabrowski , et al. |
July 5, 2022 |
Method to optimally reduce antenna array grating lobes on a
conformal surface
Abstract
In examples, systems and methods for a conformal array are
described. In one example, an array is described. The array
includes a plurality of antenna elements formed in a conformal
array. The conformal array is arranged on a non-planar surface.
Additionally, the array includes a respective feed for each of at
least a subset of the antennas of the plurality of antenna
elements. Each feed of the array is coupled to a respective antenna
of the plurality of antennas based on a taper profile determined
based on the non-planar surface. In another example, a method of
determining an antenna array is disclosed. The method includes
determining a planar array configuration for a plurality of
antennas. The method further includes mapping the planar array
configuration to a conformal surface to form a conformal array.
Additionally, the method includes determining a taper profile based
on the conformal array.
Inventors: |
Dabrowski; Ted R. (Madison,
AL), Williams; John Dalton (Decatur, AL) |
Applicant: |
Name |
City |
State |
Country |
Type |
The Boeing Company |
Chicago |
IL |
US |
|
|
Assignee: |
The Boeing Company (Chicago,
IL)
|
Family
ID: |
1000006410553 |
Appl.
No.: |
16/676,895 |
Filed: |
November 7, 2019 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20210143544 A1 |
May 13, 2021 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01Q
1/28 (20130101); H01Q 21/061 (20130101); H01Q
3/34 (20130101); H01Q 21/22 (20130101); G01S
7/2813 (20130101) |
Current International
Class: |
H01Q
1/28 (20060101); H01Q 3/34 (20060101); H01Q
21/22 (20060101); H01Q 21/06 (20060101); G01S
7/28 (20060101) |
Field of
Search: |
;342/371 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
101291016 |
|
Oct 2008 |
|
CN |
|
103606005 |
|
Feb 2014 |
|
CN |
|
106229675 |
|
Dec 2016 |
|
CN |
|
111600125 |
|
Aug 2020 |
|
CN |
|
111680414 |
|
Sep 2020 |
|
CN |
|
WO-2006016156 |
|
Feb 2006 |
|
WO |
|
Primary Examiner: Liu; Harry K
Attorney, Agent or Firm: McDonnell Boehnen Hulbert &
Berghoff LLP
Claims
What is claimed is:
1. An array comprising: a plurality of antenna elements formed in a
conformal array, wherein the conformal array is arranged on a
non-planar surface, and wherein the plurality of antenna elements
include at least one antenna having a U-shape; and a respective
feed for each of at least a subset of the antennas of the plurality
of antenna elements, wherein each feed is coupled to a respective
antenna of the plurality of antennas based on a taper profile
determined based on the non-planar surface.
2. The array of claim 1, wherein the taper profile is determined
based on a minimization of grating lobes.
3. The array of claim 1, wherein a first subset of antennas are
coupled to feeds and a second subset of antennas are not coupled to
feeds.
4. The array of claim 1, wherein the taper profile provides a
respective power level for each antenna of the plurality of
antennas.
5. The array of claim 1, wherein the taper profile provides a
respective phase for each antenna of the plurality of antennas.
6. The array of claim 1, wherein the taper profile is determined
with the antenna elements arranged in the conformal array.
7. The array of claim 1, further comprising a corporate feed
beamforming network coupled to the respective feeds for each of at
least the subset of the antennas of the plurality of antenna
elements.
8. The array of claim 1, further comprising a flexible substrate
upon which the plurality of antennas is mounted.
9. The array of claim 1, wherein the conformal array is a
two-dimensional array of antenna elements.
10. A method of determining an antenna array comprising:
determining a planar array configuration for a plurality of
antennas, wherein the plurality of antenna elements include at
least one antenna having a U-shape; mapping the planar array
configuration to a conformal surface to form a conformal array; and
determining a taper profile based on the conformal array.
11. The method of claim 10, wherein determining the taper profile
comprises determining a taper profile that causes array grating
lobes to be at or below a grating lobe threshold.
12. The method of claim 10, wherein determining the taper profile
comprises determining an enabled subset of the antennas.
13. The method of claim 10, wherein determining the taper profile
comprises determining respective power level for each antenna of
the plurality of antennas.
14. The method of claim 10, wherein determining the taper profile
comprises determining a respective phase for each antenna of the
plurality of antennas.
15. The method of claim 10, further comprising determining a
corporate feed beamforming network based on the taper profile.
16. The method of claim 10, wherein determining a planar array
comprises determining a two-dimensional array.
17. An antenna system comprising: a flexible substrate; a first
array feed; a corporate beamforming network coupled to the array
feed; and a plurality of antenna elements mounted on the flexible
substrate and formed in a conformal array, wherein the conformal
array is arranged on a non-planar surface, and wherein the
plurality of antenna elements include at least one antenna having a
U-shape.
18. The antenna system of claim 17, wherein the corporate
beamforming network is coupled to a subset of the antenna
elements.
19. The antenna system of claim 17, wherein the corporate
beamforming network is configured to provide antenna elements with
a signal based on a predetermined taper profile.
20. The antenna system of claim 19, wherein the taper profile is
determined based on the conformal array on the non-planar surface.
Description
FIELD
Embodiments of the present disclosure relate generally to antennas.
More particularly, embodiments of the present disclosure relate to
antenna structures including the associated feeding of array
structures.
BACKGROUND
Radio systems generally use antennas to transmit and receive
signals. The direction at which signals are transmitted and
received is based on a radiation pattern of the antenna. The
radiation pattern of an antenna specifies a region over which an
antenna can efficiently transmit and receive radio signals.
Some radio systems are configured having multiple antennas forming
an array of antennas. An array may be an arrangement of antennas
that have a physical layout that produces desirable antenna
properties. For example, antennas may be arranged in a linear array
with the antennas aligned on a line, a two dimensional array with
the antennas aligned on a plane, or other possible antenna array
arrangements as well. The array may have a radiation pattern that
is the superposition (i.e., sum) of the radiation patterns of the
individual antennas. In some arrays, the relative power and phasing
of various antenna elements may be adjusted in order to create a
desired radiation pattern.
SUMMARY
In one example, an array is described. The array includes a
plurality of antenna elements formed in a conformal array. The
conformal array is arranged on a non-planar surface. Additionally,
the array includes a respective feed for each of at least a subset
of the antennas of the plurality of antenna elements. Each feed of
the array is coupled to a respective antenna of the plurality of
antennas based on a taper profile determined based on the
non-planar surface.
In another example, a method of determining an antenna array is
disclosed. The method includes determining a planar array
configuration for a plurality of antennas. The method further
includes mapping the planar array configuration to a conformal
surface to form a conformal array. Additionally, the method
includes determining a taper profile based on the conformal
array.
In one yet another example, an antenna system is disclosed. The
antenna system includes a flexible substrate. The antenna system
also includes a first array feed. Additionally, the antenna system
includes a corporate beamforming network coupled to the array feed.
Yet further, the antenna system includes a plurality of antenna
elements mounted on the flexible substrate and formed in a
conformal array, wherein the conformal array is arranged on a
non-planar surface.
The features, functions, and advantages that have been discussed
can be achieved independently in various embodiments or may be
combined in yet other embodiments further details of which can be
seen with reference to the following description and drawings.
BRIEF DESCRIPTION OF THE FIGURES
Example novel features believed characteristic of the illustrative
embodiments are set forth in the appended claims. The illustrative
embodiments, however, as well as a preferred mode of use, further
objectives and descriptions thereof, will best be understood by
reference to the following detailed description of an illustrative
embodiment of the present disclosure when read in conjunction with
the accompanying drawings, wherein:
FIG. 1A illustrates an example antenna array on a flat surface.
FIG. 1B illustrates an example conformal antenna array on a curved
surface, according to an example embodiment.
FIG. 2 illustrates an example corporate feed network for feeding an
antenna array, according to an example embodiment.
FIG. 3A illustrates a top view of an example patch antenna having a
slot, according to an example embodiment.
FIG. 3B illustrates a side view of an example patch antenna having
a slot, according to an example embodiment.
FIG. 4 illustrates an example aircraft, according to an example
embodiment.
FIG. 5 is a block diagram of various systems of an aircraft.
FIG. 6 shows a flowchart of an example method of forming a
conformal array, according to an example embodiment.
FIG. 7 shows a flowchart of an example method of operating a radar
system, according to an example embodiment.
FIG. 8 shows a flowchart of an example method of operating an
antenna, according to an example embodiment.
DETAILED DESCRIPTION
Disclosed embodiments will now be described more fully hereinafter
with reference to the accompanying drawings, in which some, but not
all of the disclosed embodiments are shown. Indeed, several
different embodiments may be described and should not be construed
as limited to the embodiments set forth herein. Rather, these
embodiments are described so that this disclosure will be thorough
and complete and will fully convey the scope of the disclosure to
those skilled in the art.
As previously discussed, when operating an array, the antenna
elements may have relative power and phasing to create a desired
radiation pattern. In some instances, it may be desirable to have a
main beam having a predetermined beam width and sidelobes (i.e.,
grating lobes) that are below a sidelobe threshold. In practice,
such as in a radar system, it may be desirable for the main beam to
be relatively narrow and for sidelobes to be -15 dB (or less) with
respect to the main lobe. Sidelobes are undesirable because they
direct energy in directions other than the intended direction,
increase received signal noise from reflections, cause the
reception of unintended signals, increase clutter signals in radar
applications, etc.
In conventional arrays, the antenna array may be a linear array or
a two dimensional array on a flat surface. Determining relative
power and phasing for the antenna elements on a flat surface is
relatively straightforward based on mathematical calculations based
on the antenna array dimensions, antenna spacing, and antenna
radiation pattern. However, when the array is not on a flat
surface, such as a conformal array on a curved surface, the
mathematics for determining relative power and phasing for the
antenna elements becomes significantly more complicated. Thus,
determining relative power and phasing for the antenna elements of
a conformal array on a curved surface may not easily be represented
by a closed-form mathematical expression. The present disclosure
includes the calculation of relative power and phasing for the
antenna elements of a conformal array to produce the desired beam
width and desired sidelobe levels, and use of such conformal array
antenna elements.
Additionally, the present disclosure includes an antenna design
that may be used in a conformal array. An example antenna that is
provided as part of this disclosure is a patch antenna. The patch
antenna may be mounted on a flexible substrate. The flexible
substrate may be a single substrate upon which all the antennas of
the array are mounted. The flexible substrate may allow the antenna
array to conform to a surface of an aircraft. For example, the
flexible substrate may be mounted to an external portion of an
aircraft, such as the external metallic skin of the aircraft. By
mounting the flexible substrate in a manner conforming to the
surface of the aircraft, the array too may conform (i.e., form a
curved shape) based on a curvature of the portion of the
aircraft.
The present antenna may be a patch antenna. The patch antenna may
be mounted on a flexible substrate and the antenna itself may be
flexible as well. The antenna may be designed having a microstrip
configured to feed the antenna. Additionally, the patch antenna may
include a slot that has a length equal to 92.5% of the wavelength
at a desired frequency of operation. In some examples, the slot may
have a U shape. The U shape of the slot may cause an input
impedance of a stripline feed of the antenna to be approximately 50
Ohms at the design frequency of the antenna. Other examples are
possible as well.
The present disclosure also includes an aircraft system that, in
some examples, may incorporate an antenna or an array as previously
described. The aircraft system may include a conformal antenna
array having a flexible substrate upon which an antenna array is
formed. The array may also include radio front-end hardware
configured to up-convert signals for transmission and down-convert
received signals. The radio front-end hardware may be mounted on a
backside of the flexible substrate. The system may also include a
radar processing system coupled to the front-end radio hardware.
The radar processing system may be configured to generate and
output low-frequency radar signals to the front-end radio hardware.
Additionally, the radar processing system may be configured to
receive and process low-frequency radar signals from the front-end
radio hardware. Moreover, the system may include a renewable energy
source configured to power the radar processing system and the
radio front-end hardware. In some examples, the renewable power
source may be able to provide enough power to power both the radar
processing system and the radio front-end hardware. In other
examples, the renewable power source only provides some of the
power to power both the radar processing system and the radio
front-end hardware
Referring now to the figures, FIG. 1A illustrates an example
antenna array 100 on a flat surface. The example antenna array 100
is shown as a two dimensional array of antenna elements arranged on
a flat surface. The example antenna array 100 has antenna elements
that are aligned on a two dimensional grid on a plane. The example
antenna array 100 is representative of a conventional two
dimensional array. The example antenna array 100 includes a
plurality of antenna elements, such as driven antenna 102 and
undriven antenna 104. As shown in FIG. 1A, each element of the
example antenna array 100 is either a driven element (unshaded
circles) or undriven elements (shaded circles). Each of the antenna
elements that form the example array 100 may have the same physical
structure as each other antenna array.
In practice, the example antenna array 100 may have a taper profile
applied across the various antenna elements that form the example
antenna array 100. By controlling the taper profile, the radiation
pattern of the example antenna array may be controlled. For
example, a main-lobe beamwidth of the antenna may be adjusted based
on changing the taper profile. Additionally, sidelobe levels of the
example antenna array 100 may be controlled based on the taper
profile. When the taper profile is adjusted, the sidelobe levels
produced by the operation of example antenna 100 may be reduced
below a predetermined sidelobe level limit.
In some examples, the taper profile may specify whether each
antenna should be driven (i.e., provided a signal to radiate) or
undriven (i.e., the antennas are not provided with any signals to
radiate). Additionally, because of the reciprocal nature of antenna
arrays, the taper profile similarly specifies whether each antenna
is coupled to a signal receiver or not. In other examples, a taper
profile may specify a relative power level for each antenna element
and/or a relative phase difference between respective antenna
elements. While controlling power levels and phasing to the antenna
elements may allow more fine-tuned control of the example antenna
array 100 beam characteristics, controlling power and phasing may
require more hardware and power. Thus, in some low-cost and
low-power requirement antenna configurations, it may be desirable
to use a taper profile that specifies whether each antenna is
active or not.
When an antenna array operates, the radiating pattern is a
superposition (i.e., summation) of the radiation patterns of the
antenna elements of the array. Thus, the overall radiation pattern
of the example antenna array 100 is the sum of the radiation
pattern of each antenna of the array, including the respective
taper profile for the antenna elements. Therefore, by adjusting the
taper profile, the radiation pattern of the example antenna array
100 may be controlled. In practice, an array of antenna elements
fed with the same phase will produce a radiation pattern having a
narrower and higher gain pattern than the single antenna element
radiation pattern. However, the sidelobe levels for the array may
be greater than the sidelobes for a single antenna element.
Because of the planar nature of the example array 100 and the
uniform spacing of antenna elements, the radiation pattern may be
calculated in a closed-form expression. Similarly, because the
radiation pattern may be solved with a closed-form expression, the
taper profile for the example antenna array 100 may also be
calculated to have a closed-form solution. Thus, an array designer
may use desired array properties, such as beam-width and side-lobe
levels to calculate the taper profile to generate the desired
radiation pattern.
FIG. 1B illustrates an example conformal antenna array 150 on a
curved surface, according to an example embodiment. Unlike the
example antenna array 100 of FIG. 1A, the conformal array 150 is
not on a flat plane. Rather, the antenna elements that form the
conformal antenna array 150 may be located on a curved surface.
When the antenna elements no longer lie on a two-dimensionally
planar surface, several issues arise. If the same taper profile is
applied to the conformal antenna array 150 as to the example
antenna array 100, the conformal antenna array 150 would likely
produce much higher sidelobes. Additionally, it may be
computationally intensive to determine a theoretical radiation
pattern for the conformal antenna array 150. Although these
problems exist, at present conformal arrays are designed by first
determining a tapering for a planar array, applying the taper, and
then conforming array. Thus, conformal arrays suffer from many
performance issues.
Similar to what was described with respect to the example antenna
array 100, the conformal antenna array 150 may also use a taper
profile that may specify whether each antenna should be driven
(i.e., provided a signal to radiate) or undriven (i.e., the
antennas are not provided with any signals to radiate). FIG. 1B
shows an example driven antenna 152 and an example undriven antenna
154. Additionally, a taper profile may be used that specifies a
relative phasing and power for each antenna as well. However, due
to the non-planar nature of the conformal antenna array 150,
closed-form solutions for the taper profile are not readily
calculable. Thus, the taper profile may be determined in a
different way.
As previously discussed, present conformal arrays determine a taper
profile when the array is a planar configuration, due to the
simplicity of calculating the taper profile. But, this leads to an
antenna that will generally perform poorly. Thus, the present
disclosure is directed toward producing a better performing
conformal array.
To design the conformal array 150, the designer may first design a
flat array. Designing the flat array includes selecting an antenna
element (such as the patch antenna described with respect to FIGS.
3A and 3B) for the array, choosing a number of antenna elements,
and the element spacing. In some examples, the array may be a two
dimensional array, with between 64 elements (in an 8.times.8
configuration) and 16384 elements (in a 128.times.128 array).
Once the base flat array is designed, a mapping may be used to map
the flat array to the conformal surface. In some examples, the
mapping may be a "bending" of the flat array onto the shape of the
surface to which the antenna will conform. In other examples, the
mapping may be a projection of the antenna elements into a position
that conforms to the surface. Other mappings from the flat surface
to a conformal shape are possible as well.
Once the mapping is created, the antenna may be stimulated in
software to determine a base radiation pattern. In some examples,
the antenna may be simulated using a method of moments simulation
to determine the base antenna parameters. Based on the results of
the simulation, a windowing function may be chosen. Some example
windowing functions include a Chebyshev window, Hamming window, or
other windowing function. The windowing function that is chosen may
be based on some parameters of the antenna design, such as
beamwidth, desired sidelobes, or other design criteria. The result
of the windowing function may be the taper profile.
In examples where low power and low complexity are desired, the
windowing function may include constraints that specify that
antennas may only be enabled or disabled. An array where antennas
are only enabled or disabled may be known as a sparse array. In
other examples, the windowing function may include constraints that
specify that antennas may have relative power and/or phase
adjustments.
Once the taper profile is determined, the conformal antenna array
150 may be simulated with the given taper profile. The results of
the simulation may be compared to the design criteria. If the
design criteria are met, the taper profile may be used for the
construction of the antenna. Otherwise, a different windowing
function or different constraints on the windowing function may be
used. Thus, unlike conventional conformal array designs, the
present conformal antenna array 150 determines the taper profile of
the antenna in its conformed state, not in its flat state. Thus,
overall array performance may be increased.
FIG. 2 illustrates an example corporate feed network 200 for
feeding an antenna array, according to an example embodiment. A
corporate feed is a method of feeding antennas that keeps the phase
of the signal provided to each antenna the same as each other
antenna. FIG. 2 is described in the present disclosure in the
context of transmitting signals. However, the structure of FIG. 2
may also be used with an array of antennas for receiving signals.
Additionally, for simplicity, FIG. 2 is shown in a single plane
with a linear array of antenna elements. In practice, a corporate
feed 200 may also be used with antennas that form a two-dimensional
conformal array.
As shown in FIG. 2, the corporate feed network 200 has an array of
antenna elements, antennas 202A-202D. The antennas 202A-202D may be
coupled to respective phase and amplitude controllers 204A-204B. In
some examples, the respective phase and amplitude controllers
204A-204B may be able to control the phase and/or amplitude of the
signals that are fed to the respective antennas. The respective
phase and amplitude controllers 204A-204B may each control the
phase and amplitude provided to a given antenna based on the taper
profile. In examples where the taper profile determines if an
antenna is enabled or disabled, the respective phase and amplitude
controllers 204A-204B may be switches or diodes. The respective
phase and amplitude controllers 204A-204B may either allow a signal
(or block a signal) to be fed to the associated antenna. In yet
further examples, the respective phase and amplitude controllers
204A-204B may simply be a matched load when the phase and amplitude
controllers are associated with an antenna that is disabled
according to the taper profile and may be a physical connection to
the antenna that is enabled according to the taper profile.
The respective phase and amplitude controllers 204A-204B are
coupled to metallic traces 206. The metallic traces 206 function to
route signals for transmission by the antennas and also to divide
power for transmission by the antennas. In other examples, the
metallic traces may take a different form than that shown in FIG.
2. Different examples may include different branching than the
metallic traces shown in FIG. 2.
The corporate feed network 200 may be coupled to radio front-end
hardware 208 and radar processing system 210. The radio front-end
hardware 208 may be coupled to an input feed of the corporate feed
network 200. The radio front-end hardware 208 may be configured to
provide signal up-conversion for transmitted signals and signal
down-conversion for received signals. The radio front-end hardware
may be coupled to the radar processing system 210. For transmitting
radar signals, the radar processing system may create a
low-frequency radar signal that is communicated to the radio
front-end hardware 208. The radio front-end hardware 208 may
upconvert the low-frequency radar signal to the desired
transmission frequency. For receiving radar signals, the radio
front-end hardware 208 may down-covert the received radar signals
to a low-frequency radar signal. The low-frequency radar signal may
be communicated to the radar processing system 210 for
processing.
In some examples, the radio front-end hardware 208 and the radar
processing system 210 may not be located near each other. For
example, the radio front-end hardware 208 may be mounted on a
substrate that contains the antennas 202A-202D and the corporate
feed network 200. The radar processing system 210 may be located
near a navigation system or other control system of the aircraft.
The radio front-end hardware 208 and the radar processing system
210 may be communicable coupled by a low-frequency communication
link. The radio front-end hardware 208 may include low power mixers
and signal generators. In some examples, the radio front-end
hardware 208 may be powered by a renewable power source.
FIG. 3A illustrates a top view of an example patch antenna 300
having a slot 304, according to an example embodiment and FIG. 3B
illustrates a side view of an example patch antenna 300 having a
slot 304, according to an example embodiment. The patch antenna 300
may be a single antenna element for use in the antenna arrays
described in this disclosure. Further, the patch antenna may be fed
by a corporate feed network, such as corporate feed network 200 of
FIG. 2. Additionally, the patch antenna 300 may be thin enough to
where it is flexible. Thus, the patch antenna 300 may be able to
conform to a surface (such as a rounded portion of an aircraft) to
which it is mounted. However, in other examples, patch antenna 300
may be used in situations. The patch antenna 300 may be used as a
single antenna element, such as in a cellular communication system.
In additional examples, the patch antenna 300 may be mounted on a
rigid substrate, such as a ceramic, such as those applications that
do not involved conforming to a surface. Thus, while the patch
antenna 300 may be used within the applications of this disclosure,
its applications are not limited to those of this disclosure.
The patch antenna 300 may be mounted on a substrate 308 that has a
top half 308A and a bottom half 308B. The patch antenna 300
includes a rectangular metal patch 302 having a slot 304. The metal
patch 302 may be fed by a stripline 306. In some examples, the
stripline 306 may be located in the center of the thickness of
substrate 308 where the top half 308A and bottom half 308B form a
plane. The substrate 308 may be a flexible substrate that can
conform to a curvature of the surface on which the substrate 308 is
mounted. Additionally, the substrate 308 may be large enough to
have a full antenna array and feeding structures incorporated in
it. Examples may also include a ground plane or back plane on the
bottom side of the bottom half 308B. However, in other examples,
the back plane may be formed by a metallic surface of an aircraft
when the antenna is installed on the aircraft.
The patch antenna 300 may have dimensions based on a desired
frequency of operation for the antenna. In some examples, the patch
antenna 300 may be designed to operate in the W-band (i.e., between
75 and 110 GHz). For W-band operations, the patch antenna 300 may
have a thickness of less than 10 mil, including the substrate but
not the front-end radio hardware. In some other examples, the patch
antenna 300 may be designed to operate with K-band frequencies
(i.e., between 18 and 27 GHz). For K-band operations, the patch
antenna 300 may have a thickness of less than 20 mil, including the
substrate and front-end radio hardware. However, in other examples,
a different frequency (or range of frequencies) may be used as
well. The rectangular metal patch 302 may have a length dimension
310 that is equal to three-quarters the wavelength at a desired
frequency of operation and width dimension 312 that is equal to
one-half the wavelength at a desired frequency of operation. In
some examples, the patch antenna 300 may operate over a bandwidth
of frequencies. In this case, the patch antenna 300 may be designed
with dimensions based on a frequency within the bandwidth of
frequencies, such as the middle frequency.
In some examples, the length dimension 310 and the width dimension
312 may be adjusted based on a permittivity of the substrate 308.
For example, the length dimension 310 and/or the width dimension
312 may be reduced by an amount proportional to the permittivity of
the substrate.
The rectangular metal patch 302 may have a slot 304. The slot 304
is an area that does not have metal. For example, the slot may be
etched or cut through the rectangular metal patch 302. The slot 304
may have length equal to (or approximately equal to) 92.5% of the
length of a wavelength at the frequency of operation. Because the
length of the slot 304 may be greater than the dimensions of the
rectangular metal patch 302, it may be desirable for the slot 304
to have a shape that allows it to fit on the rectangular metal
patch 302. The slot 304 may have a U-shape with two arms parallel
to the long dimension of the rectangular metal patch 302. The two
parallel arms may cause the slot 304 to have a polarization that
primarily linear. Additionally, the slot 304 may be centered on the
rectangular metal patch 302.
In order to drive the antenna, a stripline 306 may be located in
the substrate 308 and pass below the rectangular metal patch 302.
The stripline 306 may be the end of the corporate feed network
described with respect to FIG. 2. The stripline 306 may also be
aligned orthogonally to the arms of the slot 304 and cross the arms
of the slot 304 near the middle of the arms. Thus, the stripline
may be located at the center of the longer dimension of the
rectangular metal patch 302. The placement of the stripline 306
with respect to the rectangular metal patch 302 and the slot 304
may cause an input impedance of the rectangular metal patch 302 to
be approximately 50 Ohms at the design frequency. By having an
input impedance of approximately 50 Ohms the need for impedance
matching hardware or components may be mitigated.
FIG. 4 illustrates an example aircraft 400, according to an example
embodiment. The aircraft 400 is representative of any type of
aircraft, such as passenger jets, unmanned aerial vehicles,
helicopters, other types of jets, spacecraft, etc. FIG. 4 displays
examples of how a conformal arrays, such as conformal array 402A
and conformal array 402B may be placed on an aircraft. An aircraft
may feature one or more antenna arrays for use in a radar system.
While conventional arrays are flat structures that are often hidden
by radomes, the present array is a conformal array configured to
conform to the surface of the aircraft 400 upon which it is
mounted. In other examples, the conformal array may be located on
the wings, top or bottom of the fuselage, or other areas of the
aircraft as well.
As an example, a conformal array 402A may be located near the front
of the front of the aircraft. In another example, a conformal array
402B may be located near the edge of a wing of the aircraft. The
present conformal arrays may be advantageous for several reasons.
First, a conformal array may be located on a surface of an aircraft
that is not flat, thus, any surface of the aircraft may be suitable
for a conformal array. Second, conventional radar systems generally
have a flat array mounted under a radome. By using a conformal
array, the aircraft structure may be designed without the need to
create dedicated space for a radar array and radome. The conformal
array me mounted on an aircraft after the aircraft structure is
designed and built.
FIG. 5 is a block diagram of various systems of an aircraft 500.
The aircraft 500 may include an airframe 502, a propulsion system
504, renewable power system(s) 506, a radar system 508, a
navigation system 510, and other systems (not shown). The airframe
502 may be the metallic outer surface of the aircraft the
associated supporting structure. Various portions of the airframe
502 may take a curved shape. As previously discussed, curved
portions of an aircraft's structure may make it difficult to place
conventional radar antenna arrays. Thus, the present radar system
508 includes a conformal array that may be placed on a curved
surface of the airframe.
The propulsion system 504 of the aircraft may include various
different types of engines. The propulsion system 504 may include
jet engines, ramjet engines, propeller engines, turboprop engines,
as well as other types of aircraft propulsion as well. The
propulsion system 504 may function to both provide propulsion for
the aircraft, but also generate some electricity for use by various
systems of the aircraft 500.
The aircraft 500 may also include one or more renewable power
system(s) 506. The renewable power system(s) 506 may be solar power
or other another type of renewable power system. The renewable
power system(s) 506 may function to produce electricity for the
various systems of the aircraft 500. In some examples, the
renewable power system(s) 506 may also include an energy storage
unit, such as a battery. In some examples, the renewable power
system(s) 506 may supply power to the battery to store for when
power is needed. In additional examples, power generated by the
propulsion system 504 may also be stored in the energy storage
unit. In some examples, the peak power produced by the renewable
power system(s) 506 may be enough to power the radar system 508 of
the aircraft. In some other examples, the peak power produced by
the renewable power system(s) 506 may be enough to power the radar
system 508 and the navigation system 510 of the aircraft. However,
in some other examples, the radar system 508 and the navigation
system 510 may only receive a subset of their electrical needs from
the renewable power system(s) 506.
FIG. 6 shows a flowchart of an example method of forming a
conformal array, according to an example embodiment. Method 600 may
be used with or implemented by the systems shown in FIGS. 1-5.
In some instances, components of the devices and/or systems may be
configured to perform the functions such that the components are
actually configured and structured (with hardware and/or software)
to enable such performance. In other examples, components of the
devices and/or systems may be arranged to be adapted to, capable
of, or suited for performing the functions, such as when operated
in a specific manner. Method 600 may include one or more
operations, functions, or actions as illustrated by one or more of
blocks 602-606. Also, the various blocks may be combined into fewer
blocks, divided into additional blocks, and/or removed based upon
the desired implementation.
It should be understood that for this and other processes and
methods disclosed herein, flowcharts show functionality and
operation of one possible implementation of present embodiments.
Alternative implementations are included within the scope of the
example embodiments of the present disclosure in which functions
may be executed out of order from that shown or discussed,
including substantially concurrent or in reverse order, depending
on the functionality involved, as would be understood by those
reasonably skilled in the art.
At block 602, the method 600 includes determining a planar array
configuration for a plurality of antennas. The planar array
configuration may be determined in part based on a set of
performance criteria for the antenna array. As previously
discussed, it may be desirable to have a main beam having a
predetermined beam width and sidelobes (i.e., grating lobes) that
are below a sidelobe threshold. In practice, such as in a radar
system, it may be desirable for the main beam to be relatively
narrow and for sidelobes to be -15 dB (or less) with respect to the
main lobe. Sidelobes are undesirable because they direct energy in
directions other than the intended direction, increase received
signal noise from reflections, cause the reception of unintended
signals, increase clutter signals in radar applications, etc. Thus,
a planar array may be designed to meet the given design criteria
and cause a minimization of grating lobes.
The array may specify a number of antennas, a radiation pattern for
a given antenna of the array, and a layout for the antennas in the
array. In some examples, determining a planar array may include
determining a two-dimensional array. A two-dimensional array may
have antennas aligned in a grid pattern having a length and width.
Additionally, the antennas may have a spacing that is uniform along
both dimensions of the array.
At block 604, the method 600 includes mapping the planar array
configuration to a conformal surface to form a conformal array.
Once the base planar array is designed at block 602, a mapping may
be used to map the flat array to the conformal surface. In some
examples, the mapping may be a "bending" of the flat array onto the
shape of the surface to which the antenna will conform. In other
examples, the mapping may be a projection of the antenna elements
into a position that conforms to the surface. Other mappings from
the flat surface to a conformal shape are possible as well.
At block 606, the method 600 includes determining a taper profile
based on the conformal array. Once the mapping is created at block
604, the antenna may be stimulated in software to determine a base
radiation pattern. In some examples, the antenna may be simulated
using a method of moments simulation to determine the base antenna
parameters of the radiation pattern, such as sidelobe levels and
beam width. Based on the results of the simulation, a windowing
function may be chosen. Some example windowing functions include a
Chebyshev window, Hamming window, or other windowing function. The
windowing function that is chosen may be based on some parameters
of the antenna design, such as beamwidth, desired sidelobes, or
other design criteria. In some examples, determining the taper
profile includes determining a taper profile that causes array
grating lobes to be at or below a grating lobe threshold causing a
minimization of grating lobes. The result of the windowing function
may be the taper profile.
In examples where low power and low complexity are desired, the
windowing function may include constraints that specify that
antennas may only be enabled or disabled. An array where antennas
are only enabled or disabled may be known as a sparse array. Thus,
in some examples, determining the taper profile includes
determining an enabled subset of the antennas. Additionally,
creating a sparse array may also include determining a corporate
feed beamforming network based on the taper profile. In some
examples, the corporate feed may include routing signals only to
the enabled antennas. In other examples, the corporate feed may
include routing signals only to all the antennas of the array. In
this example, each antenna may have an associated switching element
that may be able to control if each antenna is enabled or disabled.
Thus, the switches (e.g., diodes or another electrical component)
may control if antennas are enabled or disabled.
In additional examples, the windowing function may include
constraints that specify that antennas may have relative power
and/or phase adjustments. Thus, in some examples, determining the
taper profile may also include determining respective power level
for each antenna of the plurality of antennas. Additionally, in
examples determining the taper profile includes determining a
respective phase for each antenna of the plurality of antennas. In
these examples, each antenna may have an associated element that
may be able to control relative power and/or phase for each
antenna. Thus, the electrical components may control the relative
power and/or phase for each antenna. In another example, the feed
structure may be a modified corporate feed to provide the
determined power and/or phase for each antenna.
Once the taper profile is determined, the conformal antenna array
may again be simulated with the given taper profile. The results of
the simulation may be compared to the design criteria. If the
design criteria are met, the taper profile may be used for the
construction of the antenna. Otherwise, a different windowing
function or different constraints on the windowing function may be
used. Thus, unlike conventional conformal array designs, the
present conformal antenna array determines the taper profile of the
antenna in its conformed state, not in its flat state. Thus,
overall array performance may be increased.
FIG. 7 shows a flowchart of an example of a method 700 of operating
a radar system, according to an example embodiment. Method 700 may
be used with or implemented by the systems shown in FIGS. 1-5.
In some instances, components of the devices and/or systems may be
configured to perform the functions such that the components are
actually configured and structured (with hardware and/or software)
to enable such performance. In other examples, components of the
devices and/or systems may be arranged to be adapted to, capable
of, or suited for performing the functions, such as when operated
in a specific manner. Method 700 may include one or more
operations, functions, or actions as illustrated by one or more of
blocks 702-710. Also, the various blocks may be combined into fewer
blocks, divided into additional blocks, and/or removed based upon
the desired implementation.
It should be understood that for this and other processes and
methods disclosed herein, flowcharts show functionality and
operation of one possible implementation of present embodiments.
Alternative implementations are included within the scope of the
example embodiments of the present disclosure in which functions
may be executed out of order from that shown or discussed,
including substantially concurrent or in reverse order, depending
on the functionality involved, as would be understood by those
reasonably skilled in the art.
At block 702, the method 700 includes providing power to a radar
processing system and a radio front-end hardware from a renewable
power source. The aircraft to which the radar system forms a part
may have a means of generating renewable power. In some examples,
the renewable energy source includes solar panels. Other
aircraft-based sources of renewable power are possible as well. In
some examples, a power requirement of the radar processing system
and the radio front-end hardware is less than the power supplied by
the renewable energy source. Thus, the renewable power source may
be able to supply all the power needed by the radar system. In some
examples, the renewable power source may be coupled to a battery or
other electrical storage device. In these examples, power generated
by the renewable power source may be stored by the battery or
energy storage device may be stored for later use.
At block 704, the method 700 includes creating a low-frequency
signal for transmission by the radar processing system and
communicating the low-frequency signal to the radio front-end
hardware. The radar processing system may be configured to create
signals for transmission by the radar system. The signals may
include a desiring signaling mode for the radar system. The signals
created by the radar processing system may be low-frequency
signals. These low frequency radar signals may be communicated from
the radar processing system to the radio front-end hardware located
on the substrate of the antenna array. By communicating
low-frequency signals, transmission losses may be mitigated.
In some examples, the radar processing system may be located near
other computational devices of the aircraft, for example, a
navigation system. The radar processing system may be in
communication with the navigation system (or other systems of the
aircraft) in order to provide data that may be used for navigation
of the aircraft.
At block 706, the method 700 includes upconverting the
low-frequency signal to a radar signal by the radio front-end
hardware. The radio front-end hardware may be located on a backside
of a flexible substrate. The radio front-end hardware may be
low-power to reduce the energy usage and heat produced by the radio
front-end hardware. The radio-front end hardware may include mixers
(or similarly functioning electronic components) configured to
upconvert the frequency of the signal from the radio processing
system. In some examples, upconverting the low-frequency signal
includes upconverting the low-frequency signals to a radar signal
having a K-band frequency. In other examples, upconverting may be
to W-band frequencies. Other frequencies may be used as well.
Additionally, when the radio front-end hardware is coupled to the
substrate, the structure of the substrate, including the radio
front-end hardware and antennas, has a thickness of 60 mils or
less. In some other examples, the structure of the substrate,
including the radio front-end hardware and antennas, has a
thickness of 20 mils or less. By keeping the thickness relatively
thin, the flexibility of the substrate may be maintained.
Additionally, in some examples, the radio front-end hardware may be
located in a way to reduce the impact on the flexibility of the
substrate.
At block 708, the method 700 includes coupling the radar signal to
a corporate feed beamforming network. When the radar signal is
coupled to the corporate feed beamforming network, the corporate
feed beamforming network may split the power in order to feed the
antennas of the array. As previously discussed, the corporate feed
beamforming network may be a modified corporate feed that provides
adjustments to the phase and amplitude of the signals for each
respective antenna, based on the taper profile. In other examples,
each antenna may have an associated component that can enable or
disable a respective antenna, based on the taper profile. In yet
another example, each antenna may have an associated component that
can adjust a relative phase and/or amplitude of a respective
antenna, based on the taper profile. Additionally, in some
examples, at least a portion of the corporate feed beamforming
network is located on a center plane of the flexible substrate. A
backplane of the flexible substrate may be a metallic surface of
the aircraft to which the array conforms.
At block 710, the method 700 includes radiating the radar signal by
an antenna array coupled to the corporate feed beamforming network.
The antenna array may be located on a front side of the flexible
substrate. As previously discussed, the flexible substrate may be
mounted to conform to a curved surface of an aircraft.
Additionally, the corporate feed beamforming network is configured
to flex along with the flexible substrate. At block 710, only a
subset of the antennas of the array may radiate a signal, based on
the taper profile.
Although method 700 is described with respect to transmitting
signals, the method may also be performed in the reverse order for
receiving signals. When performed in the reverse order, the antenna
array may receive reflected radar signals. The radar signals
received by the array may be routed through the corporate feed
network to the radio front-end hardware. The radio front-end
hardware may be configured to downconvert the received radar
reflection signals to a low-frequency signal. These low-frequency
signals may be communicated by way of a cable to the radar
processing system. The radar processing system may be able to
determine information (i.e., location and speed) about objects that
caused the reflected through analyzing the low-frequency signals.
The information determined about the objects that cause the
reflections may be used by a navigational system of the
aircraft.
FIG. 8 shows a flowchart of an example method of operating an
antenna, according to an example embodiment. Method 800 may be used
with or implemented by the systems shown in FIGS. 1-5.
In some instances, components of the devices and/or systems may be
configured to perform the functions such that the components are
actually configured and structured (with hardware and/or software)
to enable such performance. In other examples, components of the
devices and/or systems may be arranged to be adapted to, capable
of, or suited for performing the functions, such as when operated
in a specific manner. Method 800 may include one or more
operations, functions, or actions as illustrated by one or more of
blocks 802-806. Also, the various blocks may be combined into fewer
blocks, divided into additional blocks, and/or removed based upon
the desired implementation.
It should be understood that for this and other processes and
methods disclosed herein, flowcharts show functionality and
operation of one possible implementation of present embodiments.
Alternative implementations are included within the scope of the
example embodiments of the present disclosure in which functions
may be executed out of order from that shown or discussed,
including substantially concurrent or in reverse order, depending
on the functionality involved, as would be understood by those
reasonably skilled in the art.
At block 802, the method 800 includes feeding an electromagnetic
signal to a rectangular patch antenna by a stripline located below
the rectangular patch antenna and separated from the rectangular
patch antenna by a portion of a substrate. The rectangular patch
antenna has a first dimension equal to one-half of a wavelength at
a given frequency of operation. Additionally, the rectangular patch
antenna has a second dimension equal to three-quarters of a
wavelength at the given frequency of operation. The rectangular
patch may have an input impedance that is approximately 50 Ohms at
the given frequency.
At block 804, the method 800 includes inducing an electromagnetic
field in a slot of the rectangular patch antenna. Inducing an
electromagnetic field in the slot includes inducing an
electromagnetic field in two arms of a U-shaped slot. The U-shaped
slot may be located in the center of the rectangular patch.
Additionally, the stripline crosses orthogonally to a direction of
the straight portion of the two arms of a U-shaped slot.
At block 806, the method 800 includes wherein the slot has a length
approximately equal to 0.925 of a wavelength at the given frequency
of operation, and a polarization that is substantially the same as
a polarization of the patch antenna. The length and positioning of
the slot may cause the input impedance of the patch to be
approximately 50 Ohms. Additionally, in some examples, the
stripline may be located in the center of a height dimension of the
substrate (where the height is measured in a direction orthogonal
to a plane defined by a surface of the patch). Additionally, the
combination of feeding the patch and inducing the field in the
slot, may cause the entire structure to radiate electromagnetic
energy into the region above the plane of the patch (in the
opposite direction of the substrate). Further, in some examples,
the present antenna may form an array of similar antennas, each
configured to radiate signals in a similar manner. Moreover, each
antenna may be fed by a stripline that forms a portion of a
corporate feed network, as previously described.
By the term "substantially", "about", and "approximately" used
herein, it is meant that the recited characteristic, parameter, or
value need not be achieved exactly, but that deviations or
variations, including for example, tolerances, measurement error,
measurement accuracy limitations and other factors known to skill
in the art, may occur in amounts that do not preclude the effect
the characteristic was intended to provide.
Different examples of the system(s), device(s), and method(s)
disclosed herein include a variety of components, features, and
functionalities. It should be understood that the various examples
of the system(s), device(s), and method(s) disclosed herein may
include any of the components, features, and functionalities of any
of the other examples of the system(s), device(s), and method(s)
disclosed herein in any combination or any sub-combination, and all
of such possibilities are intended to be within the scope of the
disclosure.
The description of the different advantageous arrangements has been
presented for purposes of illustration and description, and is not
intended to be exhaustive or limited to the embodiments in the form
disclosed. Many modifications and variations will be apparent to
those of ordinary skill in the art. Further, different advantageous
embodiments may provide different advantages as compared to other
advantageous embodiments. The embodiment or embodiments selected
are chosen and described in order to best explain the principles of
the embodiments, the practical application, and to enable others of
ordinary skill in the art to understand the disclosure for various
embodiments with various modifications as are suited to the
particular use contemplated.
* * * * *